Light emitting diodes (LEDs) are semiconductor light emitting devices that emit lights when an electrical current is supplied thereto. Typically, an LED is formed of multiple layers of materials having a layer of p-doped material or p-type semiconductor layer (“p-layer”), a layer of n-doped material or an n-type semiconductor layer (“n-layer”), and a light generating region or p-n junction. When powered, the p-n junction emits lights in a primary direction towards one of the p- and n-layers creating a field of illumination.
To improve light emission efficiency of an LED device, various techniques have been proposed by the prior art, examples of which follow.
U.S. Pat. No. 6,784,462, entitled “Light-emitting diode with planar omni-directional reflector” and issued to Fred E. Schubert on Aug. 31, 2004, discloses an omni-directional reflector disposed between a light-emitting region and a conductive holder. The reflector has a transparent layer, an array of ohmic contacts and a reflective conductive film, arranged in sequence. The ohmic contacts increase the portion of light that reaches and is reflected by the underlying reflective film, and the increased reflection, in turn, increases the light extraction efficiency of the LED. However, the LED of '462 patent has a relatively high requirement on the material of the reflective film, which needs to be electrically conductive and have a high reflectivity. Furthermore, the disposal of the reflector between the light-emitting region and the conductive holder may make the fabrication process unnecessarily complicated.
In U.S. Pat. No. 6,958,494, entitled “Light emitting diodes with current spreading layer” and issued to Lin, et al. on Oct. 25, 2005, a conductive and transparent Indium-Tin Oxide (ITO) film and an ultra-thin composite metallic layer, serving as a good ohmic contact and current spreading layer, are firstly attached onto a semiconductor cladding layer. Thereafter, holes may be etched into the semiconductor cladding layer to form a Photonic Band Gap structure to improve LED light extraction. However, the process of forming the Photonic Band Gap structure may be unnecessarily complicated. Furthermore, the etching process may cause damages to the contact layer above the semiconductor cladding layer and consequently may make the electrical contact instable.
It is an object of the present invention to provide a semiconductor light-emitting device, which overcomes at least some of the deficiencies exhibited by some of those of the prior art.